HAVE PHONE, KHAN TRAVELS: Learn on the go! Khan Academy has now made all of its 3,500+ YouTube videos available on the iPhone with an iPhone-compatible version of its popular iPad app. Left out of the nifty 2.6 MB app are features like video downloads, subtitles, and the badging system found on its bigger iOS brother. Users don't seem to mind: both versions are ranked in the Top 10 free educational downloads in the iTunes Store.